Oil pipelines, particularly those extending from wellheads, typically carry a mixture of oil and water, and often significant amounts of gas.
Removal of the water from the oil is desirable, and many types of separators are known in the art.
In particular, gravity separators, which rely on the higher density of water than oil for separation of the phases, are commonly used. In a conventional gravity separator, separation is usually achieved by allowing the fluid phases to have a few minutes of stagnant retention time under the influence of gravity alone. Retention time on the order of minutes necessitates large and bulky vessels to achieve separation between the liquid phases.
The most common type of water separator is a large tank separator. However, tank separators are bulky and present operational difficulties e.g. for offshore operation due to limits on available space. Furthermore, tank separators, being bulky, are typically provided as centralised facilities accepting co-mingled production from a number of pipelines. However, this means that the production pipelines which supply such separators (sometimes over long distances) are often overloaded with water and therefore larger and more costly than they need to be.
U.S. Pat. No. 5,837,152 discloses a gravity tank separator in which the tank is formed as an elongate cylinder disposed obliquely to the horizontal.
Several alternatives have been suggested to replace the dependence on conventional gravity tank separation, of which cyclonic separation and in-line separation have received considerable attention recently. Cyclonic in-line separation has been applied successfully to mixtures of two phases with highly contrasting densities, such as the case in degassing and deliquidising. In-line separation of two liquids of relatively comparable densities has also been demonstrated successfully. This latter technology offers significant advantages over conventional tank gravity separation, such as reduction in equipment size, separation while liquid is being transported, and improved emulsion breaking. However, the separation is still effectively based on gravitational settling of stagnantly retained liquids.
U.S. Pat. No. 6,755,978 discloses an apparatus for separating a first fluid from a mixture of a first and a second fluid. The apparatus has a settling chamber surrounding a production pipe for the flowing mixture. At least one aperture allows the mixture to flow into the settling chamber from the production pipe.
U.S. Pat. No. 6,719,048 discloses an apparatus for the downhole separation of water from the oil/gas in a well. Gravity is allowed to work on a non-vertical section of the well to separate fluid components, and the separated components are then pumped to the surface or into a subterranean discharge zone using separated flow paths. Detectors are used to control the pumping to keep unsettled/unseparated mixture away from the separated flow paths.
WO 02/01044 proposes an inclined separator for separating well fluids. The separator has an inlet which comprises insert tubes for well fluids, and at least two outlets for discharge of the separated fluids. The insert tubes extend from one of the ends of the separator to a longitudinally central position. The upper of the outlets is for the discharge of the lightweight fraction of the well fluids, and the lower of the outlets is for the discharge of the heavier fraction.